Observations of M82 at 5 GHz with the 5-km Radio Telescope

Abstract

The Cambridge 5-km radio telescope has been used to map M82 at 5 GHz with a resolution of 2″.0 arc in right ascension and 2″.1 arc in declination. The map reveals a source 50″ × 15″ arc in extent, with major axis close to that of the optical galaxy. Five per cent of the flux originates from a compact object < 0″.6 arc in diameter. A possible model of the source is one in which this compact object supplies relativistic electrons to the main radio-emitting region which is coextensive with the distribution of H I in the centre of the galaxy. The electrons are confined to this region by magnetohydrodynamic waves self-generated by the electrons where the density of H I becomes sufficiently low. The region has a high dust content and also a high energy density in starlight, which results in it being a strong infrared source. Inverse Compton scattering of the infrared photons by the electrons responsible for the radio emission can produce the observed X-ray emission from the direction of the source. The radiation pressure of the starlight on the dust will also be important dynamically, and may explain the observed filamentary structure along the minor axis of the galaxy.